Dataset Information

Modification of the moving point test method for nighttime eddy CO2 flux filtering on hilly and complex terrains.

ABSTRACT: The measurement of carbon dioxide (CO2) fluxes using the eddy covariance technique is difficult in forests in complex terrain because of the horizontal advection of CO2 at night. This results the under- or overestimation of net ecosystem exchanges of CO2. We propose a technique for nighttime filtering (and correction) of CO2 fluxes to eliminate (and replace) those significantly affected by horizontal advection: the modified moving point test method. This was developed by merging the friction velocity filtering and van Gorsel methods. It is based on an approach using moving windows for time and friction velocity, allowing a nighttime CO2 flux correction that includes an assessment of CO2 drainage at midnight. We tested the method using datasets from two flux towers in forests in hilly and complex terrains, where the application of generic nighttime filtering methods is difficult because CO2 drainage is generated earlier than the time assumed by the generic methods. The method produced carbon budgets consistent with previous research results, while showing improved applicability. •We propose a nighttime CO2 flux filtering method for hilly and complex terrain that combines the friction velocity filtering and van Gorsel methods.•This method determines the friction velocity threshold and the significance of CO2 drainage at midnight based on an approach using moving windows for time and friction velocity.•The method produced consistent results and shows improved applicability.

SUBMITTER: Kang M

PROVIDER: S-EPMC6541885 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Modification of the moving point test method for nighttime eddy CO2 flux filtering on hilly and complex terrains.

Kang Minseok M Kim Joon J Malla Thakuri Bindu B Chun Junghwa J Cho Chunho C

MethodsX 20190514

The measurement of carbon dioxide (CO2) fluxes using the eddy covariance technique is difficult in forests in complex terrain because of the horizontal advection of CO2 at night. This results the under- or overestimation of net ecosystem exchanges of CO2. We propose a technique for nighttime filtering (and correction) of CO2 fluxes to eliminate (and replace) those significantly affected by horizontal advection: the modified moving point test method. Th ...[more]

PMID: 31193749

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Project description:Abstract We demonstrate that an extended eddy?diffusivity mass?flux (EDMF) scheme can be used as a unified parameterization of subgrid?scale turbulence and convection across a range of dynamical regimes, from dry convective boundary layers, through shallow convection, to deep convection. Central to achieving this unified representation of subgrid?scale motions are entrainment and detrainment closures. We model entrainment and detrainment rates as a combination of turbulent and dynamical processes. Turbulent entrainment/detrainment is represented as downgradient diffusion between plumes and their environment. Dynamical entrainment/detrainment is proportional to a ratio of a relative buoyancy of a plume and a vertical velocity scale, that is modulated by heuristic nondimensional functions which represent their relative magnitudes and the enhanced detrainment due to evaporation from clouds in drier environment. We first evaluate the closures off?line against entrainment and detrainment rates diagnosed from large eddy simulations (LESs) in which tracers are used to identify plumes, their turbulent environment, and mass and tracer exchanges between them. The LES are of canonical test cases of a dry convective boundary layer, shallow convection, and deep convection, thus spanning a broad rangeof regimes. We then compare the LES with the full EDMF scheme, including the new closures, in a single?column model (SCM). The results show good agreement between the SCM and LES in quantities that are key for climate models, including thermodynamic profiles, cloud liquid water profiles, and profiles of higher moments of turbulent statistics. The SCM also captures well the diurnal cycle of convection and the onset of precipitation. Key Points An extended eddy?diffusivity mass?flux (EDMF) scheme successfully captures diverse regimes of convective motions Unified closures are presented for entrainment and detrainment across the different convective regimes With the unified closures, the EDMF scheme can simulate dry convection, shallow cumulus, and deep cumulus

Dataset Information

Modification of the moving point test method for nighttime eddy CO2 flux filtering on hilly and complex terrains.

Publications

Modification of the moving point test method for nighttime eddy CO<sub>2</sub> flux filtering on hilly and complex terrains.

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